The current invention relates to data acquisition, and more particularly to “no dead time” data acquisition for measurement instruments, such as oscilloscopes.
The “dead time” of a measurement instrument, such as an oscilloscope, is a time when data acquisition circuitry does not respond to a valid trigger event by displaying a waveform representing an electrical signal being monitored. In an analog oscilloscope, for example, dead time occurs during beam retrace time on a cathode ray tube. In a digital oscilloscope dead time often occurs when the instrument is busy with a number of tasks, i.e., not able to process a trigger when a previously acquired waveform is being read from an acquisition memory or when it is busy drawing the acquired data to make an image of the waveform for display. Electronic circuits occasionally work in an unexpected manner. The incorrect operation may be rare, perhaps occurring once in thousands of correct cycles of operation. Fast circuits that cycle quickly often operate at rates much faster than a standard digital oscilloscope can display the corresponding waveforms. The typical digital oscilloscope ignores most of the triggers because it is busy processing and drawing waveforms. The waveforms that show the incorrect operation of the circuit may be missed, i.e., may not be acquired. An oscilloscope user may have to wait a long time in order to view the incorrect operation. Even though incorrect circuit operation may not be visible, the oscilloscope user may not ever have confidence that the circuit is working properly since only a small fraction of the waveforms are drawn on the oscilloscope display. The basic digital oscilloscope has an architecture in which data is received in an acquisition memory, and then acquisition is halted by a trigger event while the acquisition memory is read and the waveform drawing is performed.
What is desired is continuous drawing of the waveform of an electrical signal so that incorrect operation of an electronic circuit being monitored, if present, is guaranteed to be drawn on the display.